🏷️ Basic Information

Make:

Yamaha

Model:

YZ125

Years Covered:

1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006

Chassis Codes:

Typical Yamaha YZ chassis codes from this era would involve alphanumeric designations, often starting with '5CF' or similar, though specific codes can vary by year and sub-model. This manual likely covers multiple chassis iterations within the 99-06 range.

👋 Introduction

Market Position:

The Yamaha YZ125 is a long-standing icon in the motocross and off-road racing world, known for its lightweight chassis, potent 125cc two-stroke engine, and agility. This manual targets owners and technicians responsible for maintaining and repairing these competitive machines.

Competitive Analysis:

During the 1999-2006 model years, the YZ125 competed directly with other premier 125cc two-stroke motocross bikes from manufacturers like KTM (125 SX), Suzuki (RM125), and Kawasaki (KX125). Its reputation for performance and reliability made it a favorite among racers and enthusiasts.

Key Features:

This manual is an exact replica of the factory service manual used by authorized Yamaha dealers. It provides the most accurate and comprehensive information necessary for proper maintenance and repair, ensuring optimal performance and longevity of the YZ125.

📋 Manual Details

Coverage Areas:

General Information, Periodic Maintenance, Fuel System, Cooling System, Engine Top End, Engine Right Side, Engine Lubrication System, Engine Removal/Installation, Crankshaft/Transmission, Wheels/Tires, Final Drive, Brakes, Suspension, Steering, Electrical System.

Page Count:

300+

Manual Type:

Factory Service Manual / Repair Manual

Language:

English

Format:

Digital Download (Factory Service Manual Download)

📖 Manual Coverage

Systems Covered:

Comprehensive coverage of all major mechanical, electrical, and chassis systems including: Engine (top-end, right-side components, lubrication, cooling, removal/installation), Fuel System (carburetor tuning, fuel delivery), Transmission, Drivetrain (final drive, chain maintenance), Brakes (front and rear hydraulic systems), Suspension (forks, rear shock, linkage), Steering, Wheels and Tires, Electrical System (wiring diagrams, ignition, lighting).

Procedures Included:

Detailed step-by-step instructions for diagnosis, inspection, repair, and overhaul. Includes troubleshooting guides for common issues, adjustment procedures, component replacement, and routine maintenance tasks. Specific procedures likely include engine disassembly/reassembly, carburetor rebuild, suspension service, brake bleeding, wheel bearing replacement, and electrical system diagnostics.

Technical Depth:

Advanced diagnostic and repair procedures, suitable for professional technicians and experienced DIY mechanics. Covers detailed specifications, torque values, clearances, and schematics for a complete understanding of the vehicle's systems.

📊 Manual Specifications

File Format:

PDF

Print Quality:

High-resolution, clear diagrams and text, suitable for printing individual pages or the entire manual.

Binding Type:

N/A (Digital Download)

Paper Type:

N/A (Digital Download)

⚙️ Engine Specifications

Engine Type:

Liquid-cooled, 125cc, two-stroke, reed-valve inducted

Bore X Stroke:

Approximately 54.0 mm x 54.5 mm (varies slightly by year/sub-model)

Compression Ratio:

Typically around 8.6:1 to 9.7:1 (varies by year/sub-model and specific tuning)

Carburetor:

Keihin PWK (e.g., PWK38S) or similar, with specific jetting and needle specifications detailed in the manual.

Horsepower:

Approx. 35-40 HP at the crank (varies by year and tuning)

Torque:

Approx. 18-20 lb-ft at the crank (varies by year and tuning)

Fuel Type:

Unleaded gasoline (premium recommended)

Fuel Oil Mix:

Pre-mix at 32:1 or 50:1 ratio with a high-quality two-stroke oil, specified in the manual.

🔧 Transmission

Transmission Type:

Constant-mesh 6-speed sequential gearbox

Optional Features:

N/A (Standard configuration for this model)

Clutch Type:

Wet, multi-disc, cable-actuated

Transmission Oil:

Yamalube SAE 10W-30 or equivalent API SE, SF service classification oil. Capacity typically around 0.7-0.8 liters.

📐 Dimensions

Overall Length:

Approx. 2175 mm (varies slightly by year)

Overall Width:

Approx. 825 mm (varies slightly by year)

Overall Height:

Approx. 1280 mm (varies slightly by year)

Dry Weight:

Approx. 90-93 kg (198-205 lbs) (varies by year)

Fuel Tank Capacity:

Approx. 7.2 - 8.0 liters (1.9 - 2.1 US gal) (varies by year)

🛡️ Safety Features

Safety Ratings:

As a competition off-road motorcycle, official safety ratings (like NHTSA or Euro NCAP) are not applicable. Safety is inherent in proper operation and maintenance, which this manual supports.

Active Features:

Disc brakes (front and rear) for effective stopping power, robust suspension for control over varied terrain.

Passive Features:

Durable frame construction, protective bodywork, and designed ergonomics to aid rider control.

💡 Technology Features

Infotainment System:

N/A (Competition off-road motorcycle, no infotainment features).

Driver Assistance Features:

N/A (Competition off-road motorcycle, no electronic driver assistance features).

Connectivity Features:

N/A (Competition off-road motorcycle, no connectivity features).

Engine Management System:

Analog CDI ignition system with mechanical power valve (YPVS).

🔧 Maintenance

Service Intervals:

This manual will detail specific intervals for: Air filter cleaning/replacement (frequent, based on usage), spark plug inspection/replacement, chain and sprockets inspection/lubrication, brake pad and fluid checks, clutch and throttle cable adjustments, engine oil changes (transmission oil), piston ring inspection/replacement (variable, based on hours/usage).

Transmission Oil Spec:

Yamalube SAE 10W-30 API SE, SF (or equivalent).

Coolant Spec:

High-quality permanent type coolant (ethylene glycol base) mixed with distilled water at a 50:50 ratio.

Brake Fluid Spec:

DOT 4 hydraulic brake fluid.

Common Issues Addressed:

The manual likely covers common wear items and potential issues such as clutch wear, carburetor jetting sensitivity to altitude/temperature, crank seal leaks, exhaust power valve operation, and suspension seal maintenance. It provides diagnostic procedures to address these.

Part Numbers:

The manual contains specific OEM part numbers for all replaceable components, crucial for ordering correct parts.

Torque Values:

Comprehensive list of all essential torque specifications for engine, chassis, and suspension fasteners, ensuring proper assembly.

📚 Vehicle History

Brand Heritage:

Yamaha has a long and storied history in motorcycle racing, particularly in motocross. The YZ line, introduced in the 1970s, has consistently been at the forefront of performance and innovation in the 125cc class.

Model Evolution 99-06:

The 1999-2006 YZ125 models represent a period of significant refinement. Key updates during this era included chassis geometry changes for improved handling, engine modifications for increased power delivery (often through YPVS - Yamaha Power Valve System advancements), updated suspension components (like KYB or Showa forks and rear shocks), and ergonomic improvements. This generation is well-regarded for its balance of power and handling.

Production Location:

Primarily manufactured in Japan by Yamaha Motor Corporation.

🏆 Awards & Recognition

Recognitions:

Throughout its production run, the Yamaha YZ125 consistently received praise in motorcycle publications and was a frequent winner in motocross shootouts and championships in its class due to its performance, handling, and reliability.